Why are all electrons the same and how do we know?


I read on an article that electrons are “all the same.” Why is that and what does that mean? How can electrons be identical? Does that apply to other elementary particles?

In: 9

All electrons have the exact same mass and charge. We know because we have measured, used, interacted with and experimented on them for a long time and havn’t found one that is different.

We don’t know that they are the same. But we haven’t found any that are different. And all measures of the size of the electron show that it is smaller than the minimum size that we can measure. So the model of all electrons being the same and being a point with no size and no substructure fits all the data we have.

electrons look same according to everything we can measure about them: size, weight, charge.

they can have different energy levels, but energy level can change, depending on how that is more about how fast they moving.

The question of “all the same” goes back to the [fundamental math](https://en.wikipedia.org/wiki/Dirac_equation) that describes how electrons behave.

The word “same” can mean a lot of things in the general English language. But in terms of the physics description linked above, the word “same” has more precise meanings.

In 1950, the physicist Schrodinger wrote his own ELI5 about that, using analogies:

The older defunct classical notion of a particle would allow you to make an analogy where 2 electrons are represented by 2 coins. Then you could say: ‘I’m putting the first coin in this first box, and the second coin in this second box.’ Or ‘I’m putting both coins in the first box’ That’d make perfect sense.

But it turns out that the [math description makes that analogy fail](https://en.wikipedia.org/wiki/Fermi%E2%80%93Dirac_statistics) when talking about electrons.

Instead, as Schrodinger wrote, the correct modern analogy for the behavior of electrons would say that two electrons are analogous to two vacancies in a group. That changes everything. Now it doesn’t make sense to say “the first vacancy” is somehow “filled twice” while the second vacancy is somehow unfilled. It also makes no sense to attach *objective* labels to two equivalent vacancies.

And that represents the aspect of “sameness” that people refer to when talking about electrons.

As Schrodinger further wrote:

> The implication, far from obvious, is that the unsuspected epithet ‘this’ is not quite properly applicable to, say, an electron, except with caution, in a restricted sense, and sometimes not at all

When you hear that they are “all the same” it means that there is no accepted theory, experimental observation or even speculative physics that suggests that one electron can be measured or used to interact differently than any other electron.

On the other hand there is no accepted theory that says all electrons *must* be identical. New physics can change this thinking.

All elementary particles in the standard model are identical in this way.